Humidifier tub



FIG. 1 is a front perspective view of a humidifier tub for a respiratory apparatus according to an embodiment of our design;

FIG. 2 is a front view thereof; and,

FIG. 3 is a top view thereof.

Where included, broken lines showing environment or structure are for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a humidifier tub, as shown and described. 